Phase diagram of the binary system PbO-Ga2O3

The phase diagram of the binary system PbO-Ga₂O₃ was determined by means of DTA and X-ray measurement. The existence of compound PbGa₂O₄ in the investigated system was confirmed. The compounds Pb₂Ga₂O₅ and PbGa₁₂O₁₉ recently published were not found.     

Phase diagram of the binary system PbOGd2O3

The phase diagram of the binary system PbOGd₂O₃ was determined by means of DTA, X-ray and high-temperature microscopy measurements. In the investigated system one stable compound Pb₄Gd₂O₇ only exists. The liquidus curves were simultaneously calculated using a thermodynamic model.     

Phase diagram of the TeO2GeO2 system

The TeO₂GeO₂ phase diagram has been investigated by X-ray phase analysis, DTA and electron microscopy. A eutectic at 67 mol% TeO₂ and 685 ± 10°C has been found. There is evidence of microscopic phase separation in some glasses.     

Phase diagram and high ionic conductivity of the system Na2WO4Ag2WO4

The phase diagram of the system Na₂WO₄Ag₂WO₄ was determined with DTA and x-ray diffractometry. The intermediate β-phase of Na₂WO₄ disappears above 0.03 mole fraction of Ag₂WO₄. The intersolubility of both compounds is good in the low temperature γ-phase of Na₂WO₄ and in the high temperature α-phase. The electrical ac conductivity was measured as a function of temperature through the phase diagram.     

Phase diagram of the LISICON,solid electrolyte system,Li4GeO4Zn2GeO4

The phase diagram of the system Li₄GeO₄Zn₂GeO₄ is fairly similar to the corresponding silicate system and contains a wide range of solid solutions that extend to either side of the composition Li₂ZnGeO₄. These solid solutions are polymorphic. The high temperature ^γII solid solutions have a crystal structure derived from that of ^γII Li₃PO₄ and a formula, Li_{2 + 2x}Zn_1?xGeO₄ : ?0.36 < x < +0.87. LISICON, x = 0.75, is one member of the ^γII solid solution series. The compositional extent of the ^γII solid solutions is temperature dependent and eg. the LISICON composition is stable as a single phase γII structure only ? 630°C. On annealing LISICON and other lithiumrich, ^γII solid solutions in the range ～100 to 600°C, various reactions occur, including 1) precipitation of Li₄GeO₄, 2) phase transition(s) to metastable low temperature, γ-derivative structure(s) and 3) atmospheric attack to give Li₂GeO₃, Li₂CO₃ and other phases. The low temperature ^βII, ^βII′ solid solutions occur over a much smaller range of compositions to either side of Li₂ZnGeO₄ and have a crystal structure derived from that of ^βII Li₃PO₄. Li₄GeO₄ forms a short range of solid solutions.     

Phase diagram of the Mn2O3Cr2O3 system in air

The phase diagram of the Mn₂O₃-Cr₂O₃ system in air within the temperature range of 1100 – 1620 K was determined by means of X-ray measurement of annealed samples. The results of the chemical analysis were employed to the estimation of the solubility of manganese ions in chromium sesquioxide.     

Phase equilibrium diagram for the system Gd2O3-MoO3

Phase equilibria have been established in the binary system Gd₂O₃MoO₃ including Gd₂(MoO₄)₃ with ferroelectricity and ferroelasticity below 159°C, by means of differential thermal analysis and X-ray powder diffraction techniques. It is shown that Gd₂(MoO₄)₃ has no solubility of other compounds in this system and melts congruently on its stoichiometric composition. Three distinct intermediate compounds were found. Gd₂O₃.6MoO₃ and Gd₂O₃.4MoO₃ are formed by a peritectic reaction at 730°C and 825°C, respectively. The remaining compound Gd₂O₃.MoO₃ with the structure closely related to Eu₂O₃.MoO₃ does not decompose below 1400°C.     

Phase relations in the CaAl2O4|CaGa2O4 system

The solid state reactions and the phase relations in the CaAl₂O₄|CaGa₂O₄ system, of which both end-members have the stuffed tridymite structure, were examined by using three kinds of starting materials; A (CaCO₃ + (Al,Ga)₂O₃), B (CaAl₂O₄ + CaGa₂O₄) and C (CaCO₃ + Al₂O₃ + Ga₂O₃). In the starting material B, a very low rate of solid state reaction between CaAl₂O₄ and CaGa₂O₄ was found, which seemed to be due to very slow interchange of Al³⁺ and Ga³⁺ located in tetrahedra of this structure. In order to obtain the probable equilibrium phase relations, it was necessary to use the starting material A. In the present system, a new phase was found in a wide range of composition as a stable phase, which was supposed to have the same structure as so-called metastable phase of CaGa₂O₄ and different array of tetrahedra from either CaAl₂O₄ or CaGa₂O₄|I.     

Photoluminescence of nanocrystalline SrMgF4 prepared by a solution chemical route

SrMgF₄ was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF₄ was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis.     

Reinvestigation of the binary diagram Na3PO4-FePO4 and crystal structure of a new iron phosphate Na3Fe3(PO4)4

A new iron(III) phosphate Na₃Fe₃(PO₄)₄ has been synthesized and characterized. It decomposes before melting at 860°C into FePO₄ and Na₃Fe₂(PO₄)₃. The structure of the compound was determined by single-crystal X-ray diffraction. The unit cell is monoclinic with the following parameters: a=19.601(8) Å, b=6.387(1) Å, c=10.575(6) Å and β=91.81(4)°; Z=4; space group: C2/c. Na₃Fe₃(PO₄)₄ exhibits a layered structure involving corner-linkage between FeO₆ octahedra, and corner- and edge-sharing between FeO₆ octahedra and PO₄ tetrahedra. The Na⁺ cations occupying the interlayer space are six- and seven-fold coordinated by oxygen atoms. The relationship between the structure of Na₃Fe₃(PO₄)₄ and the previous reported hydrate K₃Fe₃(PO₄)₄·H₂O will be discussed.     

Temperature dependence of critical stress and phase diagram of ferroelastic Pb3 (PO4)2 Pb3 (VO4)2

The temperature dependence of the critical stress in ferroelastic Pb₃ (PO₄)₂ reveals a Curie-Weiß law ($\text{ß =}\text{1}\text{2}$) up to 145°C. Between 160°C and the transition point at 180°C a crossover to a $\text{ß =}\text{1}\text{3}$ regime was found. For mixed crystals Pb₃ (PO₄)₂ ? Pb₃ (VO₄)₂ a phase diagram is suggested from optical, dielectric and Raman spectroscopical experiments.     

Phase equilibria in the system Li2O-TiO2

The system Li₂O-TiO₂ contains four stable phases: Li₄TiO₄, Li₂TiO₃, Li₄Ti₅O₁₂ and Li₂Ti₃O₇, and one metastable phase, H. Li₂TiO₃ undergoes an order-disorder phase transition at 1215°C. High Li₂TiO₃ forms an extensive range of solid solution between ～44 and 66 mole % TiO₂ and low Li₂TiO₃ forms a more limited range of solid solution between ～47 and 51% TiO₂. The temperature of the order-disorder transition decreases to either side of the Li₂TiO₃ composition. The spinel phase Li₄Ti₅O₁₂, has an upper limit of stability at 1015 ± 5°C, above which it decomposes to high Li₂TiO₃ ss and Li₂Ti₃O₇. Li₂Ti₃O₇ has a lower limit of stability at 957 ± 20°C, below which it decomposes to Li₄Ti₅O₁₂ and rutile. During this decomposition of Li₂Ti₃O₇, phase H, a metastable phase of unknown composition, forms as an intermediate. Li₂Ti₃O₇ forms a short range of solid solutions between ～74 and 76% TiO₂. A phase diagram for the system Li₂O-TiO₂ has been constructed using a combination of results determined here and those reported by GICQUEL, MAYER and BOUAZIZ. X-ray powder diffraction data are given for Li₂Ti₃O₇, Li₄Ti₅O₁₂ and phase H.     

Phase equilibrium and growth of homogeneous crystals in the γLa2S3  γNd2S3 system

T-x diagram of the γLa₂S₃  γNd₂S₃ system was plotted for the temperature interval 1400–2100°C. γLa₂S₃ and γNd₂S₃ form unlimited solid solutions of the substitution type. Basing on this phase diagram the theoretical distribution curves of Nd₂S₃ along the ingot of length were calculated. The experimental distribution curves were determined by chemical and electron microprobe measurements of La and Nd content in γ(La,Nd)₂S₃ ingots directionally solidified from the melt of different composition. Character of the component distribution in the ingots shows that diffusion of neodymium and lanthanum is exeptionally fast at 1700–2000°C. This phenomenon is explained by vacancy diffusion mechanism in γLa₂S₃  γNd₂S₃ solid solutions. Crystal structure of these solid solutions belongs to Th₃P₄ type with high concentration of randomly distributed cation vacancies.     

Spectroscopic ellipsometry study of Cu2ZnGeSe4 and Cu2ZnSiSe4 poly-crystals

We report the room temperature spectroscopic ellipsometry study of Cu₂ZnGeSe₄ and Cu₂ZnSiSe₄ crystals, grown by modified Bridgman technique. Optical measurements were performed in the range 1.2–4.6 eV. The spectral dependence of the complex pseudodielectric functions as well as pseudo- complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity of Cu₂ZnGeSe₄ and Cu₂ZnSiSe₄ crystals were derived. The observed structures in the optical spectra were analyzed by Adachi's model and attributed to the band edge transitions and higher lying interband transitions. The parameters such as strength, threshold energy, and broadening, corresponding to the E₀, E_1A and E_1B interband transitions, have been determined using the simulated annealing algorithm.     

Phase equilibrium of the VSe2/1bV3Se4 system and the thermodynamic quantities of the V3Se4 phase

The equilibrium selenium vapour pressure of V_xSe₂ (1.2 < x < 1.7) was measured by a thermobalance method at 1053, 1113 and 1163K under controlled selenium vapour pressure. The thermodynamic partial molar quantities of the V₃Se₄ phase were evaluated from the measured P_Se- X isotherms. Further, the powder X-ray and high temperature DTA measurements of the quenched specimens were carried out in order to identify the phase.     

Crystal growth of Nd: NaLu(WO4)2

Nd: NaLu(WO₄)₂ single crystals have been grown by the top seeded solution growth (TSSG) method. The peaks shown in the X-ray powder diffraction pattern were assigned. The crystal belongs to the space group of I4₁/a and the unit-cell parameters were calculated as a = b = 5.168 Å, c = 11.174 Å, V = 298.46 Å³. It is a tetragonal scheelite-like single crystal. The DSC (differential scanning calorimeter) curve proved that the as-grown crystal had a glass transition at the temperature range of 733.8 °C-781.4 °C which was lower than its melting point at 1149.3 °C. The absorption and fluorescence spectra were measured at room temperature.     

Syntheses and structures of Ta2(WO2)0.87H0.26(PO4)4 and Ta2(MoO2)(PO4)4

Tantalum hydrogen phosphate, β-TaH(PO₄)₂, has a three-dimensional structure that is stable to remarkably high temperature (∼600 °C) presumably due to the presence of strong hydrogen bonds. Impedance measurements indicate a low conductivity, 2.0 × 10⁻⁶ S/cm at 200 °C in 5% H₂. In further studies aimed at enhancing the conductivity by aliovalent doping, we have investigated systematically the synthesis of compounds in the TaH(PO₄)₂-W₂P₂O₁₁ system at 380 °C. As a result, a new phase, Ta₂(WO₂)_0.87H_0.26(PO₄)₄, was identified and subsequently the molybdenum analog Ta₂(MoO₂)(PO₄)₄ was also prepared. The structures were determined by single crystal X-ray diffraction techniques. The structures of Ta₂(WO₂)_0.87H_0.26(PO₄)₄ and Ta₂(MoO₂)(PO₄)₄ can be formally derived from the structure of β-TaH(PO₄)₂ by the replacement of two P-OH protons with an MO₂²⁺ (M = Mo and W) group together with a change in the orientation of some phosphate tetrahedra.     

Preparation and properties of the Pb3(VO4)2Pb3(PO4)2 system

Single crystals of the pseudobinary system Pb₃(V_1?xP_xO₄)₂ were grown via the Czochralski technique and were studied over wide ranges of x, particularly with regard to the influence of substitution on the $\text{3}\text{?}\text{mF}\text{2}\text{m}$ transition as a function of temperature.     

Crystal growth and spectral properties of Pr:La2(WO4)3

Pr³⁺-doped La₂(WO₄)₃ single crystal with dimensions up to Ø 20 mm × 35 mm has been grown by the Czochralski method. The structure of the Pr³⁺:La₂(WO₄)₃ crystal was determined by the X-ray powder diffraction and the Pr³⁺ concentration in this crystal was determined. The absorption and fluorescence spectra of Pr³⁺:La₂(WO₄)₃ crystal were measured at room temperature, and the fluorescence lifetime of main emission multiplets were estimated from the recorded decay curves. The spectral properties related to laser performance of the crystal were evaluated.